How should I get over the loss of my two cats and pet dog?

Well, about three years ago, we got four free kittens from the gym I was going to. There was a black and white tuxedo female (We named her Phoebe), a brown, white, and black female (We named her Piper), a brown, black and white tabby tom (We gave him to my sister and her husband and they named him Olaf), and a brown tabby tom (We gave him to my other sister and her husband and they named him Siby), and we kept Phoebe and Piper. We had them for almost two years when a personal family situation happened, and we had to let my sisters take care of them for a while. When they arrived at their houses, they both ran away after six months of being under their care. Me and my little sister cried our eyes out because we were so close to them, and I'm still having trouble getting over them. I have dreams of finding them and being so happy, and I wake up and find out it was only a dream, and then I just cry myself back to sleep. (I'm extremely dramatic).

Then, me and my mom and my brother and younger sister moved into a new place. (Before, we lived with two Jack Russell Terriers named Maddie and Amos who we've had since I was four), and we had to rent a duplex. My mom couldn't afford to keep two dogs, and my sisters already had enough animals (one sister had fifteen cats and a dog, and my other sister had two dogs and three cats, and all cats that they owned were related to Siby, Olaf and Phoebe and Piper)--so, anyways, we had to give Amos to the Humane Society. I cried my eyes out once again. This was only two months ago. Now I'm completely heartbroken. I'm thirteen, and I need help. How can I help of this ridiculous mourning of animals?